Understanding how grass species’ traits relate to their invasiveness and the invasibility of their monocultures can inform restoration of diverse grassland. We measured vegetative traits for 18 bunch grass species local to Pietermaritzburg (KwaZulu-Natal, South Africa) and measured their competitive effect on a phytometer. Using 3 m x 3 m plots planted as monocultures 12 years earlier, we related principal components of these traits to how species had invaded other species’ plots ( invasiveness), and how their monocultures had been invaded ( invasibility). Species with high total leaf mass, many tillers and low specific leaf area (SLA) were most invasive and most resistant to invasion by other grasses. Short, slow-growing grasses were most invasible by forbs. This was partly explained by linking traits to invasion through competitive effect: grasses with high total leaf mass, many tillers and low SLA showed the strongest competitive effect, which appears to be necessary but not sufficient for invasiveness. Thus, traits can predict species’ ecological performance and provide insight into the processes structuring plant communities. Restoring grasses with short stature, slow growth, low leaf mass, few tillers, and high SLA may facilitate invasion by other native species, thereby increasing species richness.